Former Secretary of State Hillary Rodham Clinton and New Jersey Gov. Chris Christie are in a dead heat in Iowa in a would-be 2016 presidential matchup, a new poll said Monday.

Both candidates take 41 percent of the vote, according to the poll released by Quinnipiac University. In a match-up against Wisconsin Gov. Scott Walker, Mrs. Clinton is ahead 7 points, 46 percent to 39 percent.

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Vice President Joseph R. Biden, who is also toying with a possible 2016 run, trails Mr. Christie badly, getting 32 percent to the Republican’s 49 percent. Mr. Walker also leads Mr. Biden, but by just a 3-point margin, 42 percent to 39 percent.

Mrs. Clinton has a favorability rating of 52 percent, compared to a 41 percent who have an unfavorable opinion. Mr. Christie has a 42-16 percent favorability rating, though 40 percent of people don’t know enough about him to form an opinion.

“Christie’s favorability ratio of almost 3-1 is impressive. The question is whether he can sustain it as he becomes better known,” said Peter Brown, assistant director of the Quinnipiac University Polling Institute. “If so, he could be a strong contender in 2016. Quinnipiac University has tested Clinton against a variety of Republicans in a number of states, and Christie seems to be running the best so far.”

Meanwhile, 55 percent of Iowa voters disapprove of the way President Obama is handling his job, compared to 41 percent who approve. Mr. Obama is heading in the wrong direction since May, when he had a 50-45 percent disapproval rating according to Quinnipiac.

The poll released surveyed 1,256 registered voters from July 15-17 and has a margin of error of 2.8 percentage points.